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原状土与重塑土在力学性质方面存在显著差别的原因,本质上在于建立在初始应力状态之上的结构性。重塑土一般是各向同性的,故在三维应力空间中其屈服曲面以等倾线为轴线。原状土由于在形成过程中一直处于三向不等压状态,故理论上讲其屈服曲面不能再以等倾线为轴线而应以初始应力线为轴线。该文以某真三轴试验为例,首先研究了特定八面体应变对应的广义剪应力随加载角的变化特征。随后,基于广义塑性力学和原状土的初始应力状态,提出了初始应力线的概念,并研究了初始应力线与等倾线的关系。进一步给出了三个适用于原状土的修正Mohr-Coulomb屈服准则,即平移模式、缩移模式和旋转模式。其中平移模式、缩移模式的屈服迹线仍然位于π平面上,而旋转模式的屈服迹线位于与初始应力线垂直的χ平面上。前两种模式可以通过等p真三轴试验结果直接对原状土的结构性进行评估;最后一种模式可以通过?1+K0?2+K0?3=c真三轴试验或等p真三轴试验数据在χ平面上的映射对原状土的结构性和各向异性进行研究。文献资料的验证表明,旋转模式修正Mohr-Coulomb屈服准则更能反映原状土的结构性,且物理意义清晰明确。
The reason that the undisturbed soil and the remolded soil have significant differences in their mechanical properties lies essentially in the structural nature of the initial stress state. Remodeling soil is generally isotropic, so its yield surface in the three-dimensional stress space equiangular axis. Since the undisturbed soil has been in a three-dimensional unequal-pressured state during its formation, theoretically its yield surface can no longer be the isostrictive axis but should be the initial stress axis. In this paper, a true triaxial test is taken as an example. Firstly, the variation characteristics of generalized shear stress with loading angle corresponding to a particular octahedral strain are studied. Subsequently, based on the generalized plastic mechanics and the initial stress state of undisturbed soil, the concept of initial stress line is proposed and the relationship between initial stress line and equiangular curve is studied. Three modified Mohr-Coulomb yield criteria, namely translation mode, shrinkage mode and rotation mode, are also given. Where the translational mode, the retrace mode yield trace is still located on the pi plane, and the spin mode yield trace is located on the χ plane perpendicular to the initial stress line. The first two modes can directly evaluate the structural properties of undisturbed soil through the true triaxial test results. The last mode can be evaluated by a true triaxial test or a true p = The mapping of the axial test data on χ-plane studies the structure and anisotropy of undisturbed soil. The verification of the literature shows that the rotation mode modified Mohr-Coulomb yield criterion can better reflect the structure of undisturbed soil, and its physical meaning is clear and definite.